Until you create this framework and prove its concept, it’s going to be an uphill battle. And I have to say the first few assets on your website are sub-standard, you need to see just how the products are made and presented on traditional 3D market places and at least have quality products setting the standard for others to draw inspiration from - especially the first few assets. Also, there is a good reason assets pertain to specific market places, i.e they are assets that are simply NOT interchangeable between engines and for those that are interchangeable, they needs to be set up with the engine specifics for that engine (are you doing that work?). Without that framework quoted above, you simply don’t have a reason at all to take any cut of an artists work.